Vehicles that utilize continuous tracks, rather than wheels are well known. These continuous tracks have several advantages over wheels. Most notably, they spread the weight of the vehicle across a greater surface area than would be practical with wheels. These tracks are provided on track assemblies that include front and rear idler wheels around which the continuous track is provided. The frame is provided with some means to hold the front and rear idler wheels, in order to place the track in tension. As the vehicle is moved along the ground, the track translates with respect to the frame, and front and rear idler wheels are rotated. Intermediate idler wheels may be used to provide additional support to the bottom span of the track, which contacts the ground. Typically, two such track assemblies are provided, laterally spaced apart, to support a cart or other vehicle.
As the cart moves across the ground, it commonly will encounter uneven areas. Typically the front and rear idler wheels are mounted to rotate in a fixed plane relative to the frame. Therefore, as the tread encounters irregularities, and especially irregularities across the width of the tread, a twisting force may result on the tread, which can result in uneven loading of the tread and the idler wheels. This problem has been partially solved by applicant's co-pending U.S. application Ser. No. 09/,847,264 by making the intermediate idler wheels pivotal in both longitudinal and lateral directions. However, the weight distribution could be further improved if the front and rear idler wheels were also designed to pivot laterally as the tread encounters uneven ground.
One complicating factor with pivoting the front idler wheels involves the need to include an alignment feature that allows adjustment of the alignment of the front idler wheel relative to the rear idler wheel. In order to compensate for small variations in the treads and the frame, it is desirable to allow some adjustment of the plane in which the front idle wheel rotates relative to the frame in order to match the plane of the rear idler wheel in order to have them properly aligned during use. This means that a simple pivoting feature for the front idler wheel may not be sufficient in all cases.
Another difficulty associated with rigidly mounted front and rear idler wheels is that because they do not pivot to match the contours of the land, the loading of the components is uneven. Therefore, the components, such as the frame, hub must be made stronger than would be required if the loading was shared equally. Therefore, the uneven loading of the parts leads to over engineering and increased costs. For example the tensioning device that holds the track in tension needs to handle a larger load if the loading of the components is not evenly distributed. That means that a larger capacity hydraulic shock must be used, or if air shocks are used, they must be inflated to a greater pressure than desired.
In order to retain the track in place on the idler wheels it is necessary to keep the track in tension. As heavier loads are added, it is desirable to increase the tension in the track. This can be done manually to compensate for a heavy or light load as it is added. However, it would be desirable to have the tension self-adjust to some extent, and to adjust as the load applied to the frame changes during travel, as for example on encountering a bump.
Therefore, a need exists to overcome one of more of the above-identified disadvantages of the current designs.